BUT....howdo the sizes run? I've never had any luck based on head circumference....always end up WAAAAY to tight....but my head is an XL in Arai, HJC, and Scorpion EXO-700.....will that be XL in FX-39??

Was writing that up now. The helmet I have is a rep sample, so it is pre-production. I am trying to find out if the unit I have is the final fit or if there are any revisions. Until I do, my comments should be considered accordingly.

Fit on this XL is much, much different and better than the FX-37. Absolutely no forehead pressure, absolutely not short front-to-back like the 37. Perhaps a little large compared to my other XL helmets, but I don't know how much use this got. I will need need thicker cheekpads for sure, and often do on other helmets.

Again, passing along fit info obligates precision, and I do not have that yet. These are just quick observations. But fit seems good, and sizing seems to fall within industry norms.